These restrictions are from Streetmap Premium data product. Generally the Streetmap Premium data product comes with help docs that describe the contents in details. If you installed it locally then the help should have also installed with it as well.

Specifically the doc for restrictions you refer to state (as the name implies) :

Avoid roads unsuitable for pedestrians - Will avoid all roads that are unsuitable for pedestrians.

My customer dont' have Streetmap Premium product and these parameters are visibile in "Closest facility" panel for setting restrictions. So he doesn't have any help documentation to understand this details.

Jay Sandhu ha scritto:

Avoid roads unsuitable for pedestrians - Will avoid all roads that are unsuitable for pedestrians.Preferred for Pedestrians - Will use preferred routes suitable for pedestrian navigation.

Don't joke with me, please: "Unsuitable" and "Preferred" are not at all explanatory.

Which are the characteristics of the roads that match this "super generic" parameters? For example: Roads without pavements?

If you use Network Analyst Online with your subscription, and you can access to this parameters through UI, it's normal that anyone of common sense want to known what does mean "unsuitable".

ESRI must complete online documentation in order to understand any parameter you can have access through UI of ArcGIS Pro.